Add Sys.isreadable, Sys.iswriteable, update ispath (JuliaLang#53320)

As discussed here:
JuliaLang#53286 (comment)

Readds the methods that were removed in
JuliaLang#12819.

base/stat.jl

@@ -326,6 +326,16 @@ otherwise returns `false`.
 This is the generalization of [`isfile`](@ref), [`isdir`](@ref) etc.
 """
 ispath(st::StatStruct) = filemode(st) & 0xf000 != 0x0000
+function ispath(path::String)
+    # We use `access()` and `F_OK` to determine if a given path exists. `F_OK` comes from `unistd.h`.
+    F_OK = 0x00
+    r = ccall(:jl_fs_access, Cint, (Cstring, Cint), path, F_OK)
+    if !(r in (0, Base.UV_ENOENT, Base.UV_ENOTDIR, Base.UV_EINVAL))
+        uv_error(string("ispath(", repr(path), ")"), r)
+    end
+    return r == 0
+end
+ispath(path::AbstractString) = ispath(String(path))
 
 """
     isfifo(path) -> Bool

base/sysinfo.jl

@@ -33,6 +33,8 @@ export BINDIR,
        iswindows,
        isjsvm,
        isexecutable,
+       isreadable,
+       iswriteable,
        username,
        which
 
@@ -556,20 +558,81 @@ const WINDOWS_VISTA_VER = v"6.0"
 
 Return `true` if the given `path` has executable permissions.
 
+!!! note
+    This permission may change before the user executes `path`,
+    so it is recommended to execute the file and handle the error if that fails,
+    rather than calling `isexecutable` first.
+
 !!! note
     Prior to Julia 1.6, this did not correctly interrogate filesystem
     ACLs on Windows, therefore it would return `true` for any
     file.  From Julia 1.6 on, it correctly determines whether the
     file is marked as executable or not.
+
+See also [`ispath`](@ref), [`isreadable`](@ref), [`iswriteable`](@ref).
 """
 function isexecutable(path::String)
     # We use `access()` and `X_OK` to determine if a given path is
     # executable by the current user.  `X_OK` comes from `unistd.h`.
     X_OK = 0x01
-    return ccall(:jl_fs_access, Cint, (Ptr{UInt8}, Cint), path, X_OK) == 0
+    return ccall(:jl_fs_access, Cint, (Cstring, Cint), path, X_OK) == 0
 end
 isexecutable(path::AbstractString) = isexecutable(String(path))
 
+"""
+    Sys.isreadable(path::String)
+
+Return `true` if the access permissions for the given `path` permitted reading by the current user.
+
+!!! note
+    This permission may change before the user calls `open`,
+    so it is recommended to just call `open` alone and handle the error if that fails,
+    rather than calling `isreadable` first.
+
+!!! note
+    Currently this function does not correctly interrogate filesystem
+    ACLs on Windows, therefore it can return wrong results.
+
+!!! compat "Julia 1.11"
+    This function requires at least Julia 1.11.
+
+See also [`ispath`](@ref), [`isexecutable`](@ref), [`iswriteable`](@ref).
+"""
+function isreadable(path::String)
+    # We use `access()` and `R_OK` to determine if a given path is
+    # readable by the current user.  `R_OK` comes from `unistd.h`.
+    R_OK = 0x04
+    return ccall(:jl_fs_access, Cint, (Cstring, Cint), path, R_OK) == 0
+end
+isreadable(path::AbstractString) = isreadable(String(path))
+
+"""
+    Sys.iswriteable(path::String)
+
+Return `true` if the access permissions for the given `path` permitted writing by the current user.
+
+!!! note
+    This permission may change before the user calls `open`,
+    so it is recommended to just call `open` alone and handle the error if that fails,
+    rather than calling `iswriteable` first.
+
+!!! note
+    Currently this function does not correctly interrogate filesystem
+    ACLs on Windows, therefore it can return wrong results.
+
+!!! compat "Julia 1.11"
+    This function requires at least Julia 1.11.
+
+See also [`ispath`](@ref), [`isexecutable`](@ref), [`isreadable`](@ref).
+"""
+function iswriteable(path::String)
+    # We use `access()` and `W_OK` to determine if a given path is
+    # writeable by the current user.  `W_OK` comes from `unistd.h`.
+    W_OK = 0x02
+    return ccall(:jl_fs_access, Cint, (Cstring, Cint), path, W_OK) == 0
+end
+iswriteable(path::AbstractString) = iswriteable(String(path))
+
 """
     Sys.which(program_name::String)
 

doc/src/base/base.md

@@ -374,6 +374,8 @@ Base.Sys.uptime
 Base.Sys.isjsvm
 Base.Sys.loadavg
 Base.Sys.isexecutable
+Base.Sys.isreadable
+Base.Sys.iswriteable
 Base.Sys.username
 Base.@static
 ```

test/file.jl

@@ -1660,23 +1660,44 @@ else
     )
 end
 
-@testset "chmod/isexecutable" begin
+@testset "chmod/isexecutable/isreadable/iswriteable" begin
     mktempdir() do dir
-        mkdir(joinpath(dir, "subdir"))
+        subdir = joinpath(dir, "subdir")
         fpath = joinpath(dir, "subdir", "foo")
 
-        # Test that we can actually set the executable bit on all platforms.
+        @test !ispath(subdir)
+        mkdir(subdir)
+        @test ispath(subdir)
+
+        @test !ispath(fpath)
         touch(fpath)
+        @test ispath(fpath)
+
+        # Test that we can actually set the executable/readable/writeable bit on all platforms.
         chmod(fpath, 0o644)
         @test !Sys.isexecutable(fpath)
+        @test Sys.isreadable(fpath)
+        Sys.iswindows() ? @test_skip(Sys.iswriteable(fpath)) : @test(Sys.iswriteable(fpath))
         chmod(fpath, 0o755)
         @test Sys.isexecutable(fpath)
+        @test Sys.isreadable(fpath)
+        Sys.iswindows() ? @test_skip(Sys.iswriteable(fpath)) : @test(Sys.iswriteable(fpath))
+        chmod(fpath, 0o444)
+        @test !Sys.isexecutable(fpath)
+        @test Sys.isreadable(fpath)
+        @test !Sys.iswriteable(fpath)
+        chmod(fpath, 0o244)
+        @test !Sys.isexecutable(fpath)
+        Sys.iswindows() ? @test_skip(!Sys.isreadable(fpath)) : @test(!Sys.isreadable(fpath))
+        Sys.iswindows() ? @test_skip(Sys.iswriteable(fpath)) : @test(Sys.iswriteable(fpath))
 
         # Ensure that, on Windows, where inheritance is default,
         # chmod still behaves as we expect.
         if Sys.iswindows()
-            chmod(joinpath(dir, "subdir"), 0o666)
-            @test Sys.isexecutable(fpath)
+            chmod(subdir, 0o666)
+            @test !Sys.isexecutable(fpath)
+            @test Sys.isreadable(fpath)
+            @test_skip Sys.iswriteable(fpath)
         end
 
         # Reset permissions to all at the end, so it can be deleted properly.